The present invention relates to improvements in a fuel vapor treatment system which effectively treats fuel vapor generated in a fuel tank, more specifically to a fuel vapor treatment system and exhaust gas purification system which purges and reforms the adsorbed fuel vapor, using water vapor, and uses the generated reformed gas containing hydrogen and carbon monoxide for the combustion or purification of exhaust gas in an internal combustion engine. It also relates to a fuel vapor treatment system and exhaust gas purification system which reforms the property of the adsorbed fuel vapor and purges generated hydrogen-rich gas before using it for the purification of exhaust gas in said internal combustion engine. Additionally, the present invention also more particularly relates to a fuel vapor recovery system by which fuel vapor generated in the fuel tank is recovered to the fuel tank.
Hitherto, a fuel vapor treatment (recovery) system has come into practical use for the purpose of preventing fuel vapor generated in a fuel tank of a vehicle from dispersing into the atmosphere. In this fuel vapor recovery system, fuel vapor, generated by a rise in the temperature of fuel in a fuel tank, for instance, is adsorbed and stored temporarily by activated carbon in a canister through a path and a fuel vapor inflow port. Then it goes through a path, having a control valve, into an induction pipe or intake air passageway by use of the negative pressure of the induction pipe of the engine so that the amount of stored fuel vapor may not exceed the adsorption capacity of the canister.
Desorption of fuel vapor from the canister will be more specifically discussed. Fuel vapor adsorbed and stored by activated carbon in the canister goes through fuel vapor exhaust port and is purged by air that is led into the canister through a gas inflow port connected to the bottom of the canister. The quantity of fuel vapor flowing into the induction pipe is controlled by a purge control valve and is burned in a combustion chamber of the engine.
However, although the fuel vapor recovery system controls the quantity of fuel vapor flowing from the path into the induction pipe, it controls gas mixed with fuel vapor that is not accurately measured and with air. Accordingly, addition of this mixed air to the accurately measured component of the combustion, which is emitted from a fuel injection valve placed upstream of the induction pipe, makes combustion difficult at the already set air-fuel ratio and causes problems, such as deterioration of driving performance of the engine and produces bad effects on the components of exhaust gas.
Also, it has been required to cut down on fuel consumption in order to deal with recent environmental problems and promote resource-saving trends. The above problems will be more apparent, if combustion at the ultra-lean air-fuel ratio (approximately 40 to 50) of air-fuel mixture to be supplied to the engine is carried out by direct fuel injection to a combustion chamber rather than the combustion at the lean air-fuel ratio (approximately 20) in the past.
On the other hand, with the improvement of combustion efficiency of the internal combustion engines, the exhaust gas temperature has been lowered and amelioration of purification efficiency of NOx at the exhaust temperature, lower than 250xc2x0 C., has been sought. An exhaust gas purification system has been demanded that can keep high efficiency in the reduction and purification of NOx under such lower exhaust gas temperature conditions .
It is an object of the present invention to provide an improved fuel vapor treatment system which can effectively overcome drawbacks encountered in conventional fuel vapor treatment systems.
Another object of the present invention is to provide an improved fuel vapor treatment system or exhaust gas purification system which can realize improvements in fuel economy (fuel consumption) and high NOx reduction efficiency under low temperature conditions, without affecting preset air-fuel ratio of air-fuel mixture to be supplied to an engine and without affecting operational characteristics of the engine and composition of exhaust gas discharged from the engine.
A further object of the present invention is to provide an improved fuel vapor treatment system which uses a membrane separation module, which does not require a vacuum pump for driving the membrane separation module and can effectively prevent fuel vapor from being emitted to the atmosphere even in case a large amount of fuel vapor is generated, without effecting operational characteristics of an engine and the composition of exhaust gas discharged from the engine even though a component passed through a separation membrane is introduced into the intake air passageway of the engine.
A first aspect of the present invention resides in a fuel vapor treatment system comprising a canister containing a fuel vapor adsorbing material and having a portion defining an inflow port through which fuel vapor from a fuel tank for an engine is flown to the fuel vapor adsorbing material, a portion defining a gas introduction port though which a purge gas for purging fuel vapor adsorbed in the fuel vapor adsorbing material is introduced into the canister, and a portion defining an outflow port through which fuel vapor purged from the fuel vapor adsorbing material is flown out of the canister. A fuel vapor treating device is provided for treating fuel vapor flown out of the canister through the outflow port so as to form a gas whose major part is other than fuel vapor. Additionally, a gas supplying or transporting device is provided to be connected to the canister, for supplying the purge gas into the canister to purge fuel vapor from the fuel vapor adsorbing material and causing the purged fuel vapor to be fed to the fuel vapor treating device. Here, the gas formed in the fuel vapor treating device is introduced into at least one of an intake air passageway and an exhaust gas passageway of the engine so as to be combusted in the engine.
A second aspect of the present invention resides in a fuel vapor recovery system comprising a canister containing a fuel vapor adsorbing material and having a portion defining an inflow port through which fuel vapor from a fuel tank of an engine is flown to the fuel vapor adsorbing material, a portion defining a gas introduction port though which a gas for purging fuel vapor adsorbed in the fuel vapor adsorbing material is introduced into the canister, and a portion defining an outflow port through which fuel vapor purged from the fuel vapor adsorbing material is flown out of the canister. A membrane separation module is provided to be connected to the canister and including a separation membrane for separating a mixture gas into an air-rich component and a fuel vapor-rich component. The separation membrane has an air-selective permeability so that the air-rich component is be able to pass through the separation membrane, the mixture gas containing air and fuel vapor. The membrane separation module has a portion defining an air-rich component discharge port through which the air-rich component is discharged out of the membrane separation module, and a portion defining a fuel-rich component discharge port through which the fuel-rich component is discharged out of the membrane separation module. Additionally, a gas transporting device is provided to be connected to the canister, for causing the purge gas to be introduced into the canister to purge fuel vapor from the fuel vapor adsorbing material and causing the purged fuel vapor to be fed to the membrane separation module. Here, the fuel vapor-rich component discharge port of the membrane separation module is connected to an intake air passageway of an engine so that vacuum generated by the engine acts on the separation membrane so as to serve as a driving force for membrane separation. Further, the air-rich component discharge port of the membrane separation module is connected to the fuel tank so that fuel vapor component contained in the fuel vapor-rich component is recovered to the fuel tank upon being subjected to at least one of liquefaction and absorption to liquid fuel in the fuel tank.
A third aspect of the present invention resides in a fuel vapor treatment system comprising a canister containing a fuel vapor adsorbing material and having a portion defining an inflow port through which fuel vapor from a fuel tank for an engine is flown to the fuel vapor adsorbing material, a portion defining a gas introduction port though which a purge gas containing steam is introduced into the canister so as to purge fuel vapor adsorbed in the fuel vapor adsorbing material, and a portion defining an outflow port through which fuel vapor purged from the fuel vapor adsorbing material and steam are flown out of the canister. A gas supplying device is provided for supplying the purge gas into the canister. Additionally, a reforming device is provided for carrying out steam reforming for fuel vapor discharged through the outflow port of the canister to form reformed gas containing hydrogen and carbon monoxide. Here, the reformed gas is introduced into an intake air passageway of the engine so as to be combusted in the engine.
A fourth aspect of the present invention resides in a fuel vapor treatment system comprising a canister containing a fuel vapor adsorbing material and including a hydrogen-enriching device for reforming fuel vapor adsorbed in the fuel vapor adsorbing material so as to form a hydrogen-rich gas, the canister having a portion defining an inflow port through which fuel vapor from a fuel tank of an engine is flown to the fuel vapor adsorbing material, a portion definin gagas introduction port though which a purge gas is introduced into the canister so as to purge fuel vapor the hydrogen-rich gas in the canister, and a portion defining an outflow port through which the purged hydrogen-rich gas is flown out of the canister. Additionally, a gas transporting device is provided for supplying the purge gas into the canister. Here, the purged hydrogen-rich gas is introduced into an exhaust gas passageway of the engine so as to purify exhaust gas of the engine.
A fifth aspect of the present invention resides in a exhaust gas purification system for an internal combustion engine, comprising a catalyst for purifying exhaust gas of the internal combustion engine. Additionally, an fuel vapor treatment system is provided including a canister containing a fuel vapor adsorbing material and having a portion defining an inflow port through which fuel vapor from a fuel tank for the engine is flown to the fuel vapor adsorbing material, a portion defining a gas introduction port though which a purge gas containing steam is introduced into the canister so as to purge fuel vapor adsorbed in the fuel vapor adsorbing material, and a portion defining an outflow port through which fuel vapor purged from the fuel vapor adsorbing material and steam are flown out of the canister. A gas supplying device is provided for supplying the purge gas into the canister. A reforming device is provided for carrying out steam reforming for fuel vapor discharged through the outflow port of the canister to form reformed gas containing hydrogen and carbon monoxide. Here, the reformed gas is introduced to the exhaust gas purifying catalyst to reduce nitrogen oxides in exhaust gas of the engine.
A sixth aspect of the present invention resides in an exhaust gas purification system for an internal combustion engine, comprising a catalyst for reducing NOx in exhaust gas of the internal combustion engine. A fuel vapor treatment system is provided including a canister containing a fuel vapor adsorbing material and including a hydrogen-enriching device for reforming fuel vapor adsorbed in the fuel vapor adsorbing material so as to form a hydrogen-rich gas, the canister having a portion defining an inflow port through which fuel vapor from a fuel tank of the engine is flown to the fuel vapor adsorbing material, a portion defining a gas introduction port though which a purge gas is introduced into the canister so as to purge fuel vapor the hydrogen-rich gas in the canister, and a portion defining an outflow port through which the purged hydrogen-rich gas is flown out of the canister. A gas transporting device is provided for supplying, the purge gas into the canister. Here, the purged hydrogen-rich gas from the hydrogen-enriching device is supplied to the NOx reducing catalyst so as to reduce nitrogen oxides and removing sulfur compound in exhaust gas of the engine.